Add listOfCodec example #1323

Job	Run time
PostGraphile mutation tests / build (12, 20.x)	3m 29s
@dataplan/pg tests / build (12, 20.x)	3m 17s
PostGraphile mutation tests (exported as graphql-js) / build (12, 20.x)	9m 57s
PostGraphile mutation tests (exported as typeDefs) / build (12, 20.x)	7m 48s
PostGraphile polymorphic query tests / build (12, 20.x)	3m 29s
PostGraphile polymorphic query tests (exported as graphql-js) / build (12, 20.x)	8m 54s
PostGraphile polymorphic query tests (exported as typeDefs) / build (12, 20.x)	6m 37s
PostGraphile v4 queries tests / build (12, 20.x)	3m 57s
PostGraphile v4 queries tests (exported as graphql-js) / build (12, 20.x)	17m 11s
PostGraphile v4 queries tests (exported as typeDefs) / build (12, 20.x)	13m 56s
PostGraphile schema tests / build (12, 20.x)	6m 42s
Small package tests / build (12, 20.x)	3m 30s
	1h 28m 47s

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